In the process of rolling a metallic workpiece, critical importance is attached to the most precise possible adjustment and maintenance of the roll gap since the final shape of the workpiece is determined thereby. At the same time, the rolling forces deflect the rolls, a factor that applies to the work rolls as well as to the intermediate and backup rolls of a roll stand. One of the classical problems in rolling flat steel is thus the roll-force-induced deflection of the set of rolls, which problem results in a greater or lesser deviation of the roll gap shape from the ideal form determined by the strip profile, and thus in deviations in flatness. A variety of solutions based on various principles have been developed to compensate for this.
DE 24 28 823 employs a spindle system that can bend the two roll chocks by displacing the spindles in two downwardly concave guide shells. This causes a bending moment to be introduced that counteracts the bending moment created by the deflection of the roll.
In DE 20 34 490, auxiliary piston-cylinder units positioned outside the center plane of the chocks are also employed that apply a bending or tilting moment to the chocks that counteracts the bending of the roll.
In DE 15 27 662 a toggle-lever-type rod arrangement is used to exert an bending moment on the two chocks of the roll, which moment again counteracts the bending moment by which the roll is bent due to the rolling force.
Axially displaceable intermediate rolls with a non-cylindrical outer surface are employed in the solution provided by DE 30 00 187 and DE 22 06 912.
Another solution using mechanical counter-bending is known from U.S. Pat. No. 1,860,931.
Currently employed rolling mills generally have at least one bending system for the work rolls, often for the intermediate rolls as well in the case of the six-high roll stand. The principle being applied is based here on introducing transverse and bending forces, and thus bending moments, into the relevant rolls. The effect, however, is generally not sufficient to compensate for the various deflection states in a rolling mill due to varying rigidity and width of the workpiece. As a result, various camber-ground rolls are used, or roll-displacement systems are provided in addition. These axial-displacement systems operate either on the principle of internal load displacement or of the modifiable equivalent crown of two rollers (so-called continuous variable crown—CVC system). The use of variably crowned rolls is cumbersome. Displacement systems are also expensive, and, particularly in response to load displacement, result in unwanted twisting of the stand. An analogous situation applies to principles that operate using slightly skewed rolls.
The common factor in all the previously known solutions is that special apparatus elements must be used to superimpose a counter-bending moment on the roll-force-induced deflection of the (work) roll. The previously known solutions are accordingly expensive and in part difficult in terms of implementation.